A Newsletter of Material Issues

By Joe Chittenden, SE, PE, LEED AP

New residential developments are sometimes constructed in noisy areas. Construction near airports or expressways or the odd Chuck E. Cheese restaurant, for example, might present significant noise‑management challenges to designers and developers. At what threshold must attention be paid to mitigating the penetration of excessive surrounding noise into residential units?

Location is obviously a significant factor, not only because of proximity to sources of exterior noise, but also because many cities and states lack ordinances or codes that require any exterior sound-transmission control for a new residential building.

A little history

In 1972, the Federal government enacted the Noise Control Act, which charged the USEPA with studying and regulating noise emissions, and the responsibility of assisting state and local government agencies in establishing their own noise regulations. The Quiet Communities Act of 1978 amended the Noise Control Act of 1972 to encourage noise-control programs at the state and community level. (Nevertheless, Congress defunded the program 1981, leaving this issue to local and state governments.)

The Aviation Safety and Noise Abatement Act of 1979 requires the FAA to develop a single system for measuring noise at airports and under certain conditions to prepare and publish noise maps.

Separately in 1971, the Department of Housing and Urban Development issued requirements for exterior noise levels, along with policies for approving HUD supported or HUD assisted housing projects located in high-noise areas. HUD has issued the Noise Guidebook to aid in determining whether such a project is located in a high-noise area.

HUD regulations set forth the following exterior‑noise standards for new housing construction:

• Exterior noise level at a proposed site of 65 decibels (dB) DNL* or less is acceptable.
• Exterior noise level at a proposed site exceeding 65 dB DNL, but not exceeding 75 dB DNL, is normally unacceptable. Appropriate sound-attenuation measures must be provided.
• Exterior noise level at a proposed site exceeding 75 dB DNL is unacceptable.

• * DNL is defined as the day-night average sound level, which is the A-weighted equivalent continuous sound-exposure level for a 24-hour period, with a 10-dB adjustment added to sound levels occurring during nighttime hours (10 pm to 7 am).

HUD's regulations do not contain standards for interior noise levels, but a goal of 45 dB is set forth. HUD outlines three methods for mitigating high noise exposures:

• Relocate the noise-sensitive uses out of the high-noise area.
• Provide a barrier, such as a wall, berm, or other building, to prevent noise reaching the site from exceeding 65 dB DNL.
• Provide a combination of a barrier and building construction to reduce the interior noise level to 45 dB DNL or less.

Are there any requirements for a residential project that is not a HUD-supported or HUD-assisted housing project?

The International Building Code provides no requirements for mitigating exterior noise. For multi-family residential construction, it only requires the following:

• Walls, partitions and floor/ceiling assemblies separating dwelling units from each other or from public or service areas are to have a sound transmission class (STC) rating of not less than 50 (45 if tested) for air‑borne noise, when tested in accordance with ASTM E 90.
• Floor/ceiling assemblies between dwelling units or between a dwelling unit and public or service area are to have an impact‑insulation‑class (IIC) rating of not less than 50 (45 if tested) for structure-borne noise, when tested in accordance with ASTM E 492.

At the state level

State governments may enact their own noise-control requirements. For instance, the 2007 California Building Code (CBC), under the section titled Exterior Sound Transmission Control, requires that "…residential structures located in noise critical areas, such as proximity to highways, county roads, city streets, railroads, rapid transit lines, airports and industrial areas, shall be designed to prevent the intrusion of exterior noises beyond prescribed levels. Proper design shall include, but shall not be limited to, orientation of the residential structures, setbacks, shielding and sound insulation of the building itself."

The CBC further states, "Interior noise levels attributable to exterior sources shall not exceed 45 dB in any habitable room." Residential structures to be located where the noise level exceeds 60 dB are to require an acoustical analysis showing that the proposed design will limit exterior noise to the prescribed interior level of 45 dB.

At the local level

Local governments may also adopt ordinances or codes that provide for noise control requirements. For example, the City of Los Angeles Building Code adopts the 2007 California Building Code with minor amendments. The City of Anaheim has a municipal code that provides exterior and interior noise standards as follows:

• Exterior noise levels within common recreation areas of multi-family projects shall be attenuated to a maximum of 65 dB CNEL*.
• Interior noise levels shall be attenuated to a maximum of 45 dB CNEL.

• * CNEL is defined as the Community Noise Equivalent Level, which is a metric similar to the DNL, except that a 5-dB adjustment is added to the equivalent continuous-sound-exposure level for evening hours (7 pm to 10 pm) in addition to the 10-dB nighttime adjustment used in the DNL.

Outside California, many large cities, such as Chicago and New York, have their own building codes. Somewhat surprisingly, these codes do not typically address any requirements for mitigating exterior noise from source(s) to site for new residential construction.

By Lisa Foster, LEED AP

Due to past construction practices, such as the use of masonry load-bearing structures, many buildings built 50 to 100 years ago have outlasted their more current counterparts. Materials like brick, concrete, and limestone, when used correctly, have proven very durable. This inherent longevity makes such structures attractive for sustainable development.

A leading source in the continued popularity growth of sustainable development has been the U.S. Green Building Council's LEED Building Certification system for New Construction, which also includes major renovations. The LEED system uses a point system to rate the sustainability of a building. Retaining over 50% of existing walls, floors, roofs, interior non-structural elements, structural elements, and building envelopes is an easy way of accruing points. Careful replacement and upgrading of certain essential components, such as windows, thermal insulation, and mechanical systems can also contribute points toward LEED certification.

One of the biggest rehabilitation trends in recent years has been the adaptive reuse and renovation of loft buildings. Converted warehouse- or factory-space-into-housing developments can be seen advertised throughout the U.S. Not to be overlooked are former schools, office buildings, banks, department stores, churches, or firehouses. In some cases, these projects can be considered historical renovations.

A historical consultant may be required and, if necessary, should be retained early in the design process. Early involvement by the consultant could prevent costly changes during the construction process.

While the use of an existing building is the basis of some serious energy savings, precautions should be taken including:

• Examine the building for potential contamination risks from hazardous materials such as asbestos, lead, and mold. Abatement work may be required prior to demolition and construction work.
• Examine the exterior walls for distress. If the existing exterior walls are masonry, survey the condition of the parapets in particular. If necessary, mortar repair, tuck pointing, and infill of damaged masonry units should be completed to prevent moisture entry during construction.
• Existing concrete slab on grade should be evaluated for serviceability, patched where necessary, and sealed to prevent moisture penetration.
• The existing roof should be inspected by a qualified roof consultant to determine whether a new roof is needed, or the extent of repairs.
• A structural engineer should determine whether repairs or reinforcement is necessary to support proposed loading increases or current code requirements.
• Determine how much of the existing finish carpentry material can be salvaged or matched by suppliers.

Reusing or refurbishing existing materials is a great way of reducing the amount of new materials being brought onsite and a creative way to earn LEED points. Existing wood floors, if in good condition, can be refinished and stained. Unique trim pieces, such as crown molding, can be infilled and painted. Finishes that can be salvaged such as doors, cabinetry, tile, and wood panels can be incorporated into the new design or made into furniture.

Obviously, many upgrades will still be necessary for continued energy and utility efficiency. These improvements could potentially gain those additional LEED points needed for certification:

• Insulated windows and new insulation at exterior walls/roof to increase the R-value.
• If the existing flat roof requires removal, consider installing additional, sloped insulation to improve thermal performance while providing positive drainage. Even applying a highly reflective coating can reduce heating loads.
• Additional flashing and waterproofing at the roof, parapets, and windows are crucial for moisture protection and can be made to match existing materials. Purchase from local suppliers to earn the LEED credit.
• Energy star rated appliances and mechanical equipment.
• Photovoltaic cells to provide a solar-powered electric supply.

With the vast number of vacant buildings available in the current real-estate market, these times provide great opportunities for rehabilitation investments. Such projects save on the costs for demolition and new construction, and extend the life of the subject building. Also, and maybe more interestingly, creative rehab constitutes an exciting method to constructing a LEED-certified project.